Scientists have been able to see closer images of the western half of the heart-shape -- known as Tombaugh Regio – on Pluto's surface, where ices appear to be moving and smoothing out the surface.

NASA said that in this area, informally named Sputnik Planum, "a sheet of ice clearly appears to have flowed – and may still be flowing -- in a manner similar to glaciers on Earth."

"We've only seen surfaces like this on active worlds like Earth and Mars," said mission co-investigator John Spencer. The ices in that region are made of nitrogen, carbon monoxide and methane.

"At Pluto's temperatures of minus-390 degrees Fahrenheit, these ices can flow like a glacier," said Bill McKinnon, deputy leader of the New Horizons Geology, Geophysics and Imaging team at Washington University in St. Louis.

"In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain has been invaded by much newer icy deposits."